1. Technical Field
The field of the currently claimed embodiments of this invention relates to blood pressure monitoring devices and methods, and more particularly to non-invasive and non-occlusive blood pressure monitoring devices and methods.
2. Discussion of Related Art
Cuff sphygmomanometer has been the gold standard for measuring blood pressure non-invasively. However, it requires the occlusion of the blood vessel by means of applying external pressure, specifically applying an unloading pressure to above the systolic pressure. Cuffs are bulky and a hassle to take on and off, and when inflated, inhibit return of venous blood to the heart and lungs. As a result, users have to stand the inconvenience and discomfort or even pain to take blood pressure measurements. These limitations of the Riva-Rocci cuff sphygmomanometer makes it unsuitable for highly frequent blood pressure monitoring.
The method used by most of the current automatic blood pressure monitors is the oscillometric waveform method, developed from cuff sphygmomanometer. It analyzes the cuff oscillation amplitudes generated by recording the cuff pressures in the process of applying an external pressure to the artery that goes above the systolic pressure and gradually bleeds down to below the diastolic pressure, and defines the systolic point at about 50% of the peak height on the rising phase of the envelope, and the diastolic point at 70% of the peak height on the falling phase of the envelope. (Baker P D, Westenskow D R, Kuck K: Theoretical analysis of non-invasive oscillometric maximum amplitude algorithm for estimating mean blood pressure. Med Biol Eng Comput 1997, 35: 271-278.) The need for high unloading pressure makes it challenging to design a low power blood pressure monitor with miniaturized components, as well as being comfortable enough to wear for repeated measurements. Thus, the current way of monitoring blood pressure still remains largely on single or very few point measurements at the clinic or at home.
Further, studies have shown that factors such as artery stiffness, cuff sizes, or arm circumferences have great impact on the accuracy of the oscillometric method. (van Popele N M, Bos W J W, de Beer N A M, van der Kuip D A M, Hofman A, Grobbee D E, Witteman J C M: Arterial stiffness as underlying mechanism of disagreement between an oscillometric blood pressure monitor and a sphygmomanometer. Hypertension 2000, 36: 484-488; Stork M, Jilek J: Cuff pressure waveforms: their current and prospective application in biomedical instrumentation. In Biomedical Engineering Trends in Electronics, Communications and Software. Edited by: Laskovski A N. InTech; 2011:193-210; Bur Al, Hirschl M M, Herkner H, Oschatz E, Kofler J, Woisetschläger C, Laggner A N: Accuracy of oscillometric blood pressure measurement according to the relation between cuff size and upper-arm circumference in critically ill patients. Crit Care Med 2000, 28(2):371-6.) A lot of clinicians question the accuracy of the automatic blood pressure monitors patients bought from pharmacies and request the patients to bring them to the clinics for calibration.
Therefore, there is unmet need for providing methods and apparatuses for comfortable, wearable, and accurate blood pressure monitoring.